The present invention is directed in general to biological enzyme-based fuel cells (a.k.a. biofuel cells) and their methods of manufacture and use. More specifically, the invention is directed to bioanodes, biocathodes, and biofuel cells comprising enzymes capable of direct electron transfer between the fuel fluid and electron conductor, and their method of manufacture and use.
A biofuel cell is an electrochemical device in which energy derived from chemical reactions is converted to electrical energy by means of the catalytic activity of living cells and/or their enzymes. Biofuel cells generally use complex molecules to generate at the anode the hydrogen ions required to reduce oxygen to water, while generating free electrons for use in electrical applications. A bioanode is the electrode of the biofuel cell where electrons are released upon the oxidation of a fuel and a biocathode is the electrode where electrons and protons from the anode are used by the catalyst to reduce peroxide or oxygen to water. Biofuel cells differ from the traditional fuel cell by the material used to catalyze the electrochemical reaction. Rather than using precious metals as catalysts, biofuel cells rely on biological molecules such as enzymes to carry out the reaction.
Most bioanodes and biocathodes include electron mediators. But, some bioanodes and biocathodes including electron mediators may have reduced lifetimes, reduced stability, unfavorable thermodynamics, and low activity of the electron mediator. Thus, a need exists for bioanodes and biocathodes that do not have the problems associated with inclusion of electron mediators.